ABSTRACT
According to dictionary definition, the word model means a miniature repre-
sentation of something; a pattern of something to be made; an example for
imitation or emulation; a description or analogy used to help visualize
something (a molecule, for instance) that cannot be directly observed; a
system of postulates, data, and inferences presented as a mathematical
description of an entity or state of affairs [1]. Consequently, modeling can
be viewed as a cognitive activity aimed at the description of how devices or
objects behave. Obviously, modeling can be performed according to different
strategies such as sketches, physical models, drawings, computer programs,
or mathematical formulas. For its generality and potentiality, however, math-
ematics often represents the selection strategy for model building. In this
light, the above-mentioned definition of a model can be particularized and the
mathematical model can be defined as a mathematical metaphor of some
aspects of reality (objects and devices behavior) [2]. This means that if A represents a determined phenomenological manifestation of reality, model
building (modeling) means to find out, inside the mathematical world, one or
more structures able to formally represent and interpret A allowing the simulation of internal A interactions and A interactions with the external environment [3]. Accordingly, the mathematical model represents the law
linking the independent variable X (usually time) to the dependent one Y (drug concentration in the blood following oral administration, for example).
Obviously, once the law is fixed, Y can assume different values in relation to the same X value by modifying model parameters. Consequently, model parameters, quantities that, by definition, neither depend on X nor on Y, allow the modification of the numerical relation between the independent and
dependent variables, the law connecting Y to X remaining the same. Therefore, if, for example, a linear relation exists between Y and X (Y ¼ mX þ q), the modification of slope m or intercept q alters the numerical Y value in relation to the same X value, being the linear law still valid.
